MPEG Motion Picture Expert Group Moving Picture Encoded Group Prateek raj gautam(725/09)
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Transcript of MPEG Motion Picture Expert Group Moving Picture Encoded Group Prateek raj gautam(725/09)
• MPEG Motion Picture Expert Group
Moving Picture Encoded Group
Prateek raj gautam(725/09)
MPEG-1 Optimized for bitrates around 1.5 Mbit/s
• mainly designed for error-free digital storage media
• multiplexing of audio, video and data• 352x240 pixels a 30 frames/sec [ NTSC based ]
• 352x288 pixels at 25 frames/sec [ PAL based ]
Applications
• CD, digital multimedia, and video database
(e.g. video-on-demand)
MPEG-2
• 2-15 or 16-80 Mbit/s bit rate
• Applications:
• satellite, cable, and terrestrial broadcasting, digital networks, and digital VCR
Basics of MPEGTypes of pictures frames
I (intra) frame
compressed using only intraframe coding
Moderate compression but faster random access
P (predicted) frame
Coded with motion compression using past I frames or P frames
Can be used as reference pictures for additional motion compensation
B (bidirectional) frame
Coded by motion compensation by either past or future I or P frames
D (DC) frame
Limited use: encodes only DC components of intraframe coding
FRAME SEQUENCE
MPEG Compression is Based on Processing
8 x 8 Pixel Blocks
Only Moving Areas Have to Be Coded
MOTION VECTOR
MOTION VECTOR
• Try to match each block in the actual picture to content in the previous picture. Matching is made by shifting each of the 8 x 8 blocks of the
• Two successive pictures pixel by pixel each direction -> Motion vector
• Substract the two blocks -> Difference block
• Transmit the motion vector and the difference block
MPEG: Video Encoding
Preprocessing
FrameMemory
+ -
DCT
MotionCompensation
MotionEstimation
FrameMemory
+
IDCT
Quantizer(Q)
Regulator
VLCEncoder
BufferQ-1
Output
Input
Pre
dict
ive
fram
e
Mot
ion
vect
ors
MPEG-2 Why another standard?
Support higher bit rates e.g., 80-100 Mbits/s for HDTV instead of the 1.15 Mvits/s for SIF
Support a larger number of applications
The encoding standard should be a toolkit rather than a flat procedure
Interlaced and non-interlaced frame
Different color subsampling modes e.g., 4:2:2, 4:2:0, 4:4:4
Flexible quantization schemes – can be changed at picture level
Scalable bit-streams
Profiles and levels
THANK YOU